In the course of structure-activity relationships on rebeccamycin analogues, two dimers of dechlorinated rebeccamycin were synthesised with the aim to improve the interaction with DNA and in vitro antiproliferative activities. The synthesis of two dimeric compounds obtained by joining two molecules of dechlorinated rebeccamycin via the imide nitrogen is described. Melting temperature and DNase I footprinting studies were performed to investigate their interaction with DNA. Four tumour cell lines, murine L1210 leukaemia, human HT29 colon carcinoma, A549 non-small cell lung carcinoma and K-562 leukaemia, were used to evaluate the cytotoxicity of the drugs. Their effects on the cell cycle of L1210 cells were also investigated.